Heat exchanger



May 3, 1966 P. LEGRAND 3,249,154

HEAT EXCHANGER Filed Nov. 3, 1961 2 Sheets-Sheet l H 'ma 1 10o 470 May3, i966 P. LEGRAND 3,249,154

HEAT EXCHANGER Filed Nov. :5. 1961 2 Sheets-Sheet 2 United States PatentO 3,249,154 HEAT EXCHANGER Pierre Legrand, 98 Rue de Rennes, Paris 6,France Filed Nov. 3, 1961, Ser. No. 149,928 Claims priority, applicationFrance, Nov. 23, 1960, 844,720; June 7, 1961, 864,173 1 Claim. (Ci.165-164) This invention relates essentially to heat exchangers andnotably to heat exchangers of the type comprising a nest of parallellongitudinally aligned Itubes adapted Ifor eecting heat transferibetween Ia heat exchanging medium passing through the interior of saidtubes and an external iluid tilowing in a generally longitudinaldirection through said nest along the external surf-aces of said tubes.

A primary object of this invention is to promote the efficiency of =aheat exchanger of the type referred to by creating a secondarytransverse movement vof the external fluid, namely, by introducingbetween adjacent -tubes helically wound strip means adapted to impart agyratory motion to said tiuid.

It is lanother object of this invention to promote the efficiency of aheat exchanger of the type referred to by forming on the tube integraliin means extending substantially transversely thereof, with a view toincrease the area of said tubes in contact with said fluid, and t-opromote and maintain said gyratory motion.

It is a further object of this invention t-o provide a heat exchanger`of the type referred to, having a compact 'and reliable structure.

The heat exchanger according to lthis invention comprises a nest oflongitudinally extending parallel tubes .adapted for the passagetherethrough of the heat exchange medium to effect heat ytransferbetween said medium and an external -uid circulating in a -generallylongitudinal direction through said nest alon-g the external surfaces ofsaid tubes. The outer surfaces of said tubes are peripherally grooved toIfor-m on said surfaces integral tn means extending substantiallytransversely of said tubes. The tubes are arranged in an yarray of rowsand columns such that `the axes of said tubes respectively detine aregular triangular lmesh pattern in which a tube in :any one row forms aregular triangle with -two adjacent tubes, -at least one `of which liesin an adjacent row. vOn the outer surface of selected tubes areprovide-d helically wound strip means, Iwhile the remainder f the tubesare bare or plain. The tubes with the strip means are selected such thateach plain tube is surrounded by tubes with strip -means thereon and ineach row there is alternately disposed a plain tube .and Itwo tubesVwith strip means thereon. Moreover, the strip means are helically woundin opposite directions on adjacent tubes, each strip means contactingthe outer surface of an `adjacent tube such .that each tube with stripmeans thereon is disposed between a bare tube and a tube with stripmeans thereon which is Wound in an opposite direction, while each baretube is disposed between two tubes with strip means thereon which arewound in opposite directions.

Further objects and features of the invention will become apparent fromthe following description taken with reference to the attached drawingin which:

FIGURE 1 illustrates diagrammatically in cross section one portion of anest of heat exchange tubes according to the invention,

FIGURE 2 is a diagramrnatical side elevational view showing one row oftubes as taken along arrows II-II in FIG. 1,

FIGURE 3 is a detail view, with parts shown in axial section, of one end.of the nest illustrated in FIGS. 1 and 2, and

4.adapted to impart a gyratory motion to the iluid.

"ice

FIGURE 4 is a cross-section taken along line lV-IV of FIG. 3.

According to a preferred embodiment of the invention as illustrated inthe drawing, a heat exchanger comprises a triangular mesh nest. iln thisrespect the nest is considered to be comprised of bare tubes lilarranged in an .array of rows and columns such that the axes of thetubes 10 respectively dene a regular triangular mesh pattern in which atube in Iany row for-ms a regular triangle with two adjacent tubes, atleast one of which lies in an adjacent row. A iluid medium circulatesexternally of the tubes in a generally longitudinal direction, forexample -from top :to bot-tom, and contacts the walls of the tubes whichare formed with relatively shall-0W peripheral grooves extendingtransversely. In order to improve the efliciency of Ithe heat exchangera rotary motion is imparted to the circulating duid in each streamformed between adjacent tubes 1@ by interposing between the tubesfurther tubes similar to those of tubes 10 but having wound and securedthereon a fiat, spiral-forming strip In the embodiment illustrated inFIGURE l there is interposed between adjacent tubes 10 tube 11 similarto tubes 1t) but having wound and secured thereon, for example by spotwelding, a dat forming strip 12. This strip `12 extends preferablynormally to the surface of the tube on ywhich it is wound and secured.From FIGURE 1, it will be seen that the width of strip 12 is such thatits outer edge engages the wall of the tubes 10. In the mesh consistingof the two tubes 10 located respectively in the lower left-hand cornerand in the center of IFIG. 1 and of the tube 10 of which only one halfis visible in the middle of the lower border of the tigure, there isdisposed another tube 114 having wound thereon a spiral-forming strip 1Sof which the pitch is opposite to .that of spiral 12. With thisarrangement, the tluid streams circulating from top to bottom willobviously be forced along a transverse lgyratory path shown by thearrows of FIG- URE 1 and 2. Since the pitches of the spiral strips haveopposite directions on adjacent tubes such as 11 .and 14 or 14 and 16,it is possible as shown in FIG. -2 to imbri- `cate the strips associatedwith these tubes and to bring the strips in contact with the outer wallsof the adjacent tubes, `whether these tubes themselves are provided withstrips or not. Thus, a compact tubular nest is obtained, wherein thetubes bear against one another and are thus protected against vibration.As shown in FIGURE l, `the num-ber and cross-sectional area of verticalby-pass passages through ywhich the fluid might flow directly withoutproducing the necessary heat exchanges are relatively low.

The heat exchanger structure as hereinabove described could beconsidered as well in terms of an array of tubes. Indeed, any one of thetubes shown in FIG. \1 pertains to three angularly equidistant rows oftubes, such as the row along line II--II shown in elevational view inFIG. l2. In each row a bare tube, such as -tube ,10, is located betweentwo tubes such as tubes 11-17, `14, 19 or `1li-18, provided :withiin-like strip means wound helically thereon according to Ioppositepitches respectively. Similarly, tube 11 is disposed between a bare tube10 and a tube provided with opposite pitch helical strip means, such astubes 14 or '18, according .to the row being considered.

The heat exchanger structure as shown could be fur- .ther described byyconsidering tha-t any one of the tubes shown in lFIG. 1 is surroundedby six adjacent tubes, and that these seven tubes constitute a unit meshof ,the heat exchanger nest.

From a mere consideration of the figure, it will clearly appear that ineach such mesh, the central tube, whether it is bare or provided withleft-hand or right-hand helical strip means, is surrounded by six tubesin a particular arrangement. 'By way of example, the bare tube 10located centrally of FIG. l is surrounded by -tubes 11, 16 and v19,provided with lefthand wound helical strip means 12 and by tubes .14, 17and .18 provided .with right-hand wound fhelical strip means 15, Whereaseach tube with a strip means thereon is surrounded by alternating baretubes and tubes with strip means thereon in which the latter are allwound in opposite direction with respect to the strip means on thecentral tube.

FIGURES 3 and 4 illustrate the manner in which Ithe seven tubes 10, 11,14 land 16-19 constituting a central hexagonal mesh in FIG. l areinterconnected at their upper and/or lower ends in the case of avertical heat exchanger, the tube end portions being left plain afterthe formation of the ns, splines, ribs, grooves or low-pitch threadstherein. The central 4tube -10 has six circular ports formed Itherein,these ports being disposed as shown by `diarnetrally opposite pairs inthree superposed planes intersecting the tube axis at 60-degreeintervals, the necks of the bent ends of tubes |11, y1&1, 16, 17, 18 and19 being welded on the wall of the central tube `10, as shown.

As shown in FIGS. l and "2 the main portion of each tube has ttedtherein a cylindrical core such as a, Illa, s17a, etc. in a cylindricalor tubular core such `as 11a, 10a, 17a closed at top and bottom by astreamlined, water-tight or nearly water-tight tip portion as shown at11b, 1Gb and 17b in FdG. 3. Thus, the cross-sectional area of theannular space formed between the tubes 1/1 and 11a, 10 and 10a, 17 and17a corresponds substantially to that of the tapered and -bent endportions of these tubes which connect the latter to the central tube 10.

With this arrangement the six mesh-forming tubes can be connected to thecentral tube by means of slightly tapered end portions withoutrestricting the cross-sectional area available for the passage of theinner tluid. This arrangement is particularly valuable in the case ofnuclear reactors wherein the number of welds should be as small aspossible.

IFor properly wedging the central ltubular core in the tubes andimproving the heat exchange, it is advantageous to provide a tube, braidor spiral-wound strip of a width of thickness substantially equal to theradial dimension `of the annular space left between the outer surface of.the core and the inner surface of the tube. The provision of thisspiral or coil-wound distance-piece ensures a proper stabilization incase of a vertical heat exchanger in which the water reheat followed bythe water vaporization and rlinally the superheating of the steam thusproduced are accomplished sequentially at different levels. By providinga non-sealed central tubular core, that is, a tubular core more or lessopen at its ends, this specic operation is improved since it is possibleto constitute within this core a make-up reserve of water which, duringthe operation of the heat exchanger, has a temperature increasinggradually from bottom to top up to vaporization temperature.

The construction of the device just described is particularly convenientif tubes 4having end portions are used with a view to form the taperedtips mentioned hereinabove to permit the proper connection of the tubeconstituting one mesh with the main or central tube.

FIGURE 4 illustra-tes by Way `of example this hexagonal distribution ofthe six tubes 11, 14, 161, 17, 118 and 19 about the central tube 10.1

Of course, this invention is also concerned with a tubular nest having asquare pattern.

Although the present invention has been described in conjunction with apreferred embodiment, it is to be understood that modilcationsy andvariations may be resorted to without departing from the spirit andscope of Ithe invention, as those skilled in the art will readilyunderstand. Such modications and variations are considered to be withinthe purview and scopeof the invention if defined by .the appended claim.

What I claim is:

A heat exchanger comprising a plurality of longitudinally extendingparallel tubes adapted for the passage therethrough of a heat exchangemedium, said tubes being arranged in an array of rows and columns suchthat the axes of said tubes in any lone row forms a regular trianglewith two adjacent tubes at least one of which lies -in an adjacent row,said tubes being adapted for the passage along .the external surfacesthereof of a second heat exchange medium, said tubes having peripheraltransverse grooves in the .outer surfaces thereof, said groovesextending substantially perpendicular to the longitudinal direction ofthe tubes, helically wound strip means on the outer surface of selectedtubes, the remainder being plain, said tubes with the strip means beingselected such that each plain tube is surrounded by tubes with stripmeans thereon and in each row there are alternately disposed a plaintube and two tubes with strip means thereon, said strip means beinghelically Wound in opposite directions on adjacent tubes each stripmeans contacting the outer surface of an adjacent tube, such that eachtube with strip means thereon is disposed between a plain tube and atube with strip means thereon which is wound in an opposite direction,While each plain tube is disposed between .two tubes with strip meansthereon which are wound in cpposi-te directions.

References Cited bythe Examiner UNITED STATES PATENTS 2,406,121 8/1946Young 165-74 2,998,228 5/1961` Huet 16S-'177 3,030,292 4/ 19162 Ritz11615-18@ 3,030,293 4/ 1962 Wyatt 165-184 3,111,168 11/1963 Huet1615-183 X FOREIGN PATENTS 3,980 4/f1-90'1 Austria. 27,6184 l11/1910Great Britain. 308,651 10/ 1955 Switzerland.

ROBERT A. OLEARY, Primary Examiner.

`CHARLES SUKALO, FREDERICK L. MAT'IESON, JR., T. W. STR-EULE, Examiners.

